The invention relates to an electric noise absorber and to a method for its fixing to an electric cable. It is known that by means of ferromagnetic material elements surrounding an electric line or cable, it is possible to reduce interference effects, particularly background electric noise.
EP 257 179 B2 discloses a noise absorber, whose ferromagnetic elements in the form of half-rings are contained in a centrally split, folding casing. At the casing through openings, through which the cable passes into and out of the casing, are fitted a plurality of teeth, which engage in the cable and fix the casing to the cable. As such noise absorbers assemblable with a cable are normally intended to be suitable for a certain cable diameter range, the teeth engage to a greater or lesser extent in the cable. The necessary clamping force must be applied on closing the casing halves. It always attempts to force the two casing halves apart and stresses the closure and the film hinges between the casing halves. In particular, this can lead to the unlocking of the casing halves, so that the two ferromagnetic material elements are not in tight engagement with one another by their joint faces, which considerably reduces the effectiveness of the noise absorber.
The applicant has therefore developed a fundamentally different system which, in place of teeth, functions with in each case a single, relatively thin, round, truncated pin, which is so flexible that it can adapt to different diameter shapes. This system operates much better than that of EP 257 179. It is intended to be further developed by the present invention.
DE 43 02 650 A1 discloses a two-part noise absorber, which has at each of the through openings in the interior of the casing two flexible cable holders, which extend via the casing parting line into the area of the facing casing half. The cable is loosely inserted between said cable holders. On closing the casing half corresponding guidance or cam faces on the other casing half act on said cable holders, bend them together and in this way firmly clamp the thus inserted line bundles. Therefore the cable holders prevent the individual conductors falling apart prior to the closing of the casing halves. However, the clamping force is here again applied through the closing of the casing halves, so that the disadvantages of the first-described construction still exist.
On assembling the noise absorber with the cable, the cable must be inserted in one of the two casing halves, so that it is located in the centrally split cable passage duct in the ferromagnetic element and consequently extends through the two casing through openings. The second casing half is then folded over and is e.g. closed by a snap-in or drop-in closure. It must be precisely ensured that the cable does not pass between the ferrite elements, which would lead to the casing bursting open or to the damage to the closure or which would make closure impossible. Thus, great attention must be paid during assembly, which is tedious.
The object of the invention is to provide an electric noise absorber and a method, which facilitates the assembly of the noise absorber with a cable and makes it independent of accidents or special skill. The casing closing function is in particular to be facilitated, while improving the casing structure.
The method according to the invention, in which the fundamental fixing of the cable takes place prior to the closing process on inserting the cable in one of the casing halves is advantageous for assembly in that the latter can be subdivided into two time-succeeding and/or place-succeeding steps, namely pressing in and therefore fixing of the cable in one casing half and the following step of closing the casing halves. The closure and the hinges between the two casing halves are not permanently influenced by the clamping force for fixing the cable. Even if, as is possible, fixing edges are provided on the second casing half shell between which the cable can be wedged, then the clamping force is limited to the moment of closing the casing half shells. To the extent that the cable has been pressed between the fixing edges, the system is once again free from forces. This in particular avoids that the force exerted by the cable on the casing and which attempts to force the latter apart, widens the gap between the ferromagnetic elements over the course of time, because plastics are known to have a slow flow under permanent force action.
Thus, the noise absorber according to the invention has fixing edges, which have a mutual spacing such that also the smallest cable for which the noise absorber is still intended, is jammed between the fixing edges on pressing in. Normally a noise absorber is intended for cables, whose diameter differs by roughly 2 mm. The spacing between the fixing edges should be e.g. 0.2 to 0.3 mm smaller than the smallest of said cable diameters. This ensures that also such a cable is well wedged and that the thickest cable can still be relatively easily pressed in. Through the complete avoidance of teeth, damage to the cable is prevented. The cable is only partly flattened and forms in its flexible insulating material two circumferentially directed, narrow flattened portions. There is no need to reduce the cable cross-section and it is instead only brought into the shape of an oval or an elongated hole, which as a result of the provision of individual, mutually insulated conductors in an insulating jacket can take place easily and without any damage. Even if force is exerted, e.g. when the noise absorber is caught on a piece of furniture on drawing through a cable, this does not lead to any damage to the cable, but at the most to a displacement of the noise absorber.
The fixing edges should be substantially parallel to one another, or at least should not diverge from parallelism than is ensured by the automatic locking of the cable between them. This also applies if the fixing edges or the strips or ledges carrying them are somewhat flexible in a certain area, e.g. the area projecting over and beyond the casing parting line. However, the flexibility must not be too great, so that the clamping force can be maintained without additional measures.
The fixing edges can be very narrow, but should not be sharp, so as to avoid damage to the cable on pressing in. The faces of the fixing edges should be straight and untoothed. However, a certain surface roughness is possible.
Preferably the fixing edges are constructed outside the actual casing, particularly outside the casing through openings. That part of the fixing edges projecting over and beyond the casing parting line plane can be free in front of the casing outer wall. The shape of the casing through openings is unimportant. When the casing is assembled they can be smooth circular and should have a diameter which at least corresponds to that of the largest intended cable. However, they also have a guidance function for the cable, so that the latter is appropriately oriented with respect to the ferromagnetic elements, but fulfil no axial fixing function. When the casing is closed the casing through openings on the open side of the two fixing edges have an additional radial securing effect.
Thus, the cable is definitively axially fixed by the fixing edges at the time of pressing in, namely by a mixed force and positive closure (due to the cable constriction). It is also radially positively fixed with respect to a degree of freedom (transverse to the fixing edges) and non-positively fixed in the direction perpendicular thereto, namely by frictional engagement between the fixing edges.
Thus, on closing the casing, during design and assembly the main attention can be directed at the matching of the casing to the optimum contact between the two seatings of the ferromagnetic elements. Thus, an easily assemblable, highly operationally reliable, efficient noise absorber is obtained.
Thus, in a preferred embodiment a noise absorber is obtained, which comprises two casing halves can be folded round a cable and containing ferrite half-rings therein. It is fixed to a cable in that prior to the closing of the casing halves is pressed between two parallel fixing edges of a fork-shaped projection on a casing end wall. The two legs of the fork project over the casing parting line, but pass externally in front of the end wall of the second casing half. The cable is laterally compressed somewhat by the substantially parallel fixing edges, which ensures a reliable longitudinal securing on the cable of the noise absorber made relatively heavy by the elements and which does not damage the cable.
Assembly is significantly facilitated in that definitive fixing takes place prior to the closing of the casing halves and no elastic bursting force remains after the folding together of the casing halves which would attempt to press the latter apart. This also ensures a good contact of the two halves of the ferrite elements, whose ring closure is particularly important for the action.
In the case of flat cables the prefixing of the cable in the casing recess and particularly the recess between the ferrite halves is particularly important. In the prior art It constantly arises that the flat cables slide between the lateral legs of the ferrite halves and consequently prevent a ring closure of the ferrite, which is important for the function.
The invention here creates a possibility of so fixing the cable to the lower casing half that on closing the casing there is no need to fear any displacement. If at all, on closing the casing only a certain clamping action is exerted on the flat cable* which inter alia ensures that the flat cable does not curve up within the noise absorber. However, the main retaining action is brought about by hook-like fixing elements, which in the manner of angle levers are in each case externally shaped onto a casing half and with a cam-like projection define a clamping gap in which can be slid the flat cable as a result of an introduction bevel. The ends of the clamping gap, which are usually bounded by the fixing element, bring about a stop action of the flat cable in the vicinity of both front faces of the casing, so that the cable is guided along the edge of the in this case flat, slot-like cable passage opening. A cam on the fixing element engages in the usually present grooves between the individual flat cable conductors and ensures a good transverse securing, while the axial securing is in part achieved by the clamping action on the flat cable and in part by a slight wavy deformation of the flat cable. As with such flat cables the insulations are particularly thin, it is important that there is no need for a penetration of the cable insulation for retention purposes.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly or in the form of sub-combinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is claimed here. The subdivision of the application into individual sections and the subtitles in no way limits the general validity of the statements made thereunder.